1. Field of the Invention
The present invention relates to electrohydraulic instruments and, more particularly, to a probe for use with a lithotriptoscope and a method of making the same.
2. Prior Art
Electrohydraulic instruments can generally be described as instruments that produce hydraulic shock waves through electrical discharges in a liquid dielectric medium. The production of shock waves by means of electrohydraulics has been put to use in lithotriptic probes for the destruction of vesical calculi or stones in the bladder, ureter and kidneys. Various different means for the treatment of stones can be found in the following U.S. Patents; U.S. Pat. No. 3,785,382 by Schmidt-Kloiber et al; U.S. Pat. No. 3,543,757 by Baler et al; U.S. Pat. No. 4,027,674 by Tessler et al; U.S. Pat. No. 3,792,701 by Kloz et al; U.S. Pat. No. 3,823,717 by Pohlman et al; U.S. Pat. No. 3,830,240 by Antonevich et al. and U.S. Pat. No. 3,413,976 by Roze.
The distal tips of electrohydraulic lithotripsy probes have generally taken two types of configurations; two electrodes arranged side-by-side or an inner electrode surrounded by an outer coaxial electrode. In both configurations, one electrode would discharge an electric current to the other electrode in the form of a flashover or dielectric breakdown through the dielectric liquid. The strength of the shockwave is generally directly proportional to the distance between the two electrodes. The greater the distance between electrodes, the greater the voltage needed to cause the breakdown of the dielectric liquid and thus, the stronger the resulting shockwave at breakdown.
However, problems exist with the probes used in the prior art. In particular, in the manufacture of probes having the inner and outer electrode configuration, it has not been possible to manufacture the two electrodes with an equispaced distance therebetween that is maintained throughout the entire work life of the probe. In the probes of the prior art, the dielectric material between the inner and outer electrodes is merely the outer covering of the inner electrode. Ordinarily, the inner electrode is a conductive wire with a soft and flexible insulation cover typical of an electrical wire. Because of the high temperatures and pressures generated at the probe distal tip, during operation of the probe, the dielectric material separating the two electrodes softens resulting in movement between the two electrodes. Failure to provide and maintain an equal distance between the inner electrode and outer electrode results in the flashover occurring along a predominate path, the shortest distance between the electrodes, rather than the desired multiple various flashover paths. The resulting predominate flashover path causes premature inner dielectric breakdown and eventual failure along the flashover line, thus causing pitting and burning at a single area. on the outer electrode reducing the working life of the probe. This reduction in the working life of the probe is typically due to two types of failures. First, the inner dielectric can experience breakdown due to more frequent flashovers about a specific point or area. These frequent concentrated flashovers form a more conductive line that allow flashovers to occur at increasingly low voltages. This results in greatly reducing the effectiveness of the shock-wave. Second, the concentrated flashovers caused by the non-centered electrodes can result in the inner dielectric experiencing actual mechanical failure such as a fracture or split of the inner dielectric material proximate the flashover line. This generally allows the inner electrode to move relative to the outer electrode decreasing the spacing between the electrodes. This decrease in spacing reduces the strength of resulting shockwaves and can eventually result in the two electrodes coming into contact and causing an electrical short with a resulting total failure of the probe.
It is an objective of the present invention to provide a probe for use with an electrohydraulic device that will have a substantially longer worklife than prior art probes.
It is a further objective of the present invention to provide a probe with an inner electrode and an outer electrode that can maintain an equispaced distance therebetween for the entire work life of the probe.
It is a further objective of the present invention to provide a quick and accurate method for producing probes with an inner electrode and outer equispaced electrode.